On October 17, 2002, David Stuart MacLean came to on a train platform in India with no idea who he was or why he was there. He had no money, no passport, no identity. It turned out that the commonly prescribed malarial medication he had been taking caused him to develop a severe form of amnesia. When he returned to the United States, he struggled to piece together the fragments of his former life. He writes about his harrowing experience in The Answer to the Riddle Is Me: A Memoir of Amnesia. We're re-airing this interview today; it was originally broadcast in January.